Manually unroll rh shader

data/shaders/rh.frag

@@ -32,26 +32,10 @@ vec4 DirToSh(vec3 dir, float flux)
     return SHBasis (dir) * flux;
 }
 
-void main(void)
+void loop(in int i,
+          in vec3 RHcenter,in vec3 RHCellSize, in vec2 RHuv, in float RHdepth,
+          inout vec4 SHr, inout vec4 SHg, inout vec4 SHb)
 {
-    vec3 normalizedRHCenter = 2. * vec3(gl_FragCoord.xy, slice) / resolution - 1.;
-    vec3 RHcenter = (RHMatrix * vec4(normalizedRHCenter * extents, 1.)).xyz;
-
-    vec4 ShadowProjectedRH = RSMMatrix * vec4(RHcenter, 1.);
-
-    vec3 RHCellSize = extents / resolution;
-    vec2 RHuv = .5 * ShadowProjectedRH.xy / ShadowProjectedRH.w + .5;
-    float RHdepth = .5 * ShadowProjectedRH.z / ShadowProjectedRH.w + .5;
-
-    vec4  SHr = vec4(0.);
-    vec4  SHg = vec4(0.);
-    vec4  SHb = vec4(0.);
-
-    int x = int(gl_FragCoord.x), y = int(gl_FragCoord.y);
-    float phi = 30. * (x ^ y) + 10. * x * y;
-
-    for (int i = 0; i < SAMPLES; i++)
-    {
     // produce a new sample location on the RSM texture
     float alpha = (i + .5) / SAMPLES;
     float theta = 2. * 3.14 * 7. * alpha;
@@ -83,7 +67,28 @@ void main(void)
     SHr += DirToSh(RSM_to_RH_dir, color.r);
     SHg += DirToSh(RSM_to_RH_dir, color.g);
     SHb += DirToSh(RSM_to_RH_dir, color.b);
-    }
+}
+
+void main(void)
+{
+    vec3 normalizedRHCenter = 2. * vec3(gl_FragCoord.xy, slice) / resolution - 1.;
+    vec3 RHcenter = (RHMatrix * vec4(normalizedRHCenter * extents, 1.)).xyz;
+
+    vec4 ShadowProjectedRH = RSMMatrix * vec4(RHcenter, 1.);
+
+    vec3 RHCellSize = extents / resolution;
+    vec2 RHuv = .5 * ShadowProjectedRH.xy / ShadowProjectedRH.w + .5;
+    float RHdepth = .5 * ShadowProjectedRH.z / ShadowProjectedRH.w + .5;
+
+    vec4  SHr = vec4(0.);
+    vec4  SHg = vec4(0.);
+    vec4  SHb = vec4(0.);
+
+    int x = int(gl_FragCoord.x), y = int(gl_FragCoord.y);
+    float phi = 30. * (x ^ y) + 10. * x * y;
+
+    loop(0, RHcenter, RHCellSize, RHuv, RHdepth, SHr, SHg, SHb);
+    loop(1, RHcenter, RHCellSize, RHuv, RHdepth, SHr, SHg, SHb);
 
     SHr /= 3.14159 * SAMPLES;
     SHg /= 3.14159 * SAMPLES;